The Story of Evolution 81 



3 . 



Evolution of Parental Care 



Mammals furnish a crowning instance of a trend of evolution 

 which expresses itself at many levels the tendency to bring forth 

 the young at a well-advanced stage and to an increase of parental 

 care associated with a decrease in the number of offspring. There 

 is a British starfish called Luidia which has two hundred millions 

 of eggs in a year, and there are said to be several millions of eggs 

 in conger-eels and some other fishes. These illustrate the spawn- 

 ing method of solving the problem of survival. Some animals 

 are naturally prolific, and the number of eggs which they sow 

 broadcast in the waters allows for enormous infantile mortality 

 and obviates any necessity for parental care. 



But some other creatures, by nature less prolific, have found 

 an entirely different solution of the problem. They practise 

 parental care and they secure survival with greatly economised 

 reproduction. This is a trend of evolution particularly character- 

 istic of the higher animals. So much so that Herbert Spencer 

 formulated the generalisation that the size and frequency of the 

 animal family is inverse ratio to the degree of evolution to which 

 the animal has attained. 



Now there are many different methods of parental care 

 which secure the safety of the young, and one of these is called 

 viviparity. The young ones are not liberated from the parent 

 until they are relatively well advanced and more or less able to 

 look after themselves. This gives the young a good send-off in 

 life, and their chances of death are greatly reduced. In other 

 words, the animals that have varied in the direction of economised 

 reproduction may keep their foothold in the struggle for exist- 

 ence if they have varied at the same time in the direction of 

 parental care. In other cases it may have worked the other way 

 round. 



In the interesting archaic animal called Peripatus, which has 



VOL. I 6 



